Why use nuclear power?
Unlike burning fossil fuels, using nuclear fission to generate electricity produces no soot or greenhouse gases. This helps keep the skies clean and doesn't contribute to global warming. The World Nuclear Association estimates that the electricity industry would add 2.6 billion tons of carbon dioxide to the atmosphere each year if it used coal power instead of nuclear.
Some governments also like nuclear power because it reduces their dependency on foreign oil.
Finally, the fuel used to power nuclear reactors is very compact in comparison to fossil fuels. For instance, one pound of uranium can supply the same energy as 3 million pounds of coal. This makes it attractive for use in nuclear-powered vehicles like submarines, aircraft carriers and spacecraft.
How much of the world's electricity comes from nuclear power?
Sixteen percent of the world's electricity is supplied by nuclear power, according to the World Nuclear Association. The electricity is produced by 440 nuclear reactors in 31 countries.
The United States has the most reactors with a total of 104, according to the International Atomic Energy Agency. The reactors are responsible for producing nearly 20 percent of the country's electricity.
The country that gets the highest percentage of its electricity from nuclear power is France. Its 59 reactors generate more than 78 percent of its electricity.
How does a nuclear power plant produce electricity?
A nuclear power plant is basically a steam power plant that is fueled by a radioactive element, like uranium. The fuel is placed in a reactor and the individual atoms are allowed to split apart. The splitting process, known as fission, releases great amounts of energy. This energy is used to heat water until it turns to steam.
From here, the mechanics of a steam power plant take over. The steam pushes on turbines, which force coils of wire to interact with a magnetic field. This generates an electric current.
Why does splitting a uranium atom release energy?
The answer has to do with Einstein's most famous equation -- E=mc² -- which essentially says that energy is directly related to mass.
Under the right conditions, a uranium atom will split into two smaller atoms and throw off two or sometimes three neutrons in the process. (Neutrons are the glue that hold atoms together.)
The combined mass of these resulting particles tends to be roughly 99.9 percent of the mass of the original uranium atom. The other 0.1 percent of the original mass got converted to energy, as Einstein described.
The energy is released in the form of gamma rays. These rays are similar to X-rays and can cause burns, cancer and genetic mutations in living things. They can be slowed or stopped with thick walls of concrete, lead or packed dirt.
Where do the extra neutrons go when the atom splits?
The neutrons hit other atoms in the reactor core, starting a chain reaction. Initially, about 3 or 4 percent of the uranium atoms are uranium-235 -- the same as the first set of atoms that split. If these atoms are hit with neutrons, they split readily and throw off more energy and neutrons.
But the other 96 or 97 percent of the uranium atoms in the core initially are of a type that is hard to split, known as uranium-238. If hit with a neutron, a uranium-238 atom will absorb the neutron and eventually turn into plutonium-239. It's not until these plutonium atoms are hit again with more neutrons that they finally split and release energy.
What is nuclear waste?
Nuclear waste is the spent nuclear fuel from a reactor. The fuel is considered spent when the fission byproducts -- the atoms left over from the splitting process -- prevent free neutrons from splitting more uranium or plutonium. It takes three or four years to get to this point in the process.
The waste is highly radioactive, so it must be stored in steel-lined concrete pools or in dry caskets.
As of 2003, nuclear reactors in the United States had created about 49,000 tons of waste, according to the Department of Energy.
Some countries, like Japan and France, reprocess their nuclear waste to extract the unspent uranium-235 and plutonium-239. This can be returned to use in nuclear power plants or used to create a nuclear bomb.
The United States has not reprocessed nuclear waste since the 1970s. Instead, the country hopes eventually to bury all its waste deep in Yucca Mountain in the Nevada desert, where officials believe the waste will not be able to leak into the environment.
What are thorium-fueled reactors, and how are they different from uranium-fueled reactors?
Scientists are trying to perfect ways to use the element thorium to fuel reactors instead of uranium because it is three times more abundant in nature. It also leaves behind less nuclear waste, and that waste is harder to exploit for use in nuclear weapons.
Also, thorium reactors produce less waste because, in a nuclear chain reaction, thorium atoms break down into fewer unusable atoms than does uranium.
In addition, with the right design, thorium-fueled reactors generate 80 percent fewer plutonium-239 atoms -- a key ingredient in atomic bombs. The reactors do produce another possible weapons material, uranium-233, but it is difficult to separate from the other, highly radioactive uranium isotopes that surround it.
In fact, a thorium-fueled reactor could actually eat up existing stockpiles of plutonium by using it as a "seed" fuel. A seed is necessary because it's harder to start a nuclear chain reaction with thorium than with uranium.
Say, what does uranium cost these days, anyway?
The average price for a pound of "yellowcake" uranium in 2004 was $12.61, according to the Energy Information Administration. Yellowcake, however, must be turned into a gas and enriched to produce the quality of uranium required for a nuclear reactor.
